The present invention relates to a method for X-ray fluoroscopy or radiography as well as an X-ray apparatus and more particularly, to a technique which is suitable for three-dimensionally measuring a large view field such as human chest in an X-ray computerized tomography (CT) scan method and an X-ray CT apparatus.
As a prior art method for measuring an X-ray fluoroscopic or radiographic image from a plurality of directions to observe or record a stereoscopic dynamic image, a rotational digital angiography (DA) or a rotational digital subtraction angiography (DSA) is described in a journal entitled "Toshiba Medical Review", No. 45, pages 2 to 11, 1992. In the journal, a C arm is provided at its one end with an X-ray image intensifier which is positioned opposed to an X-ray tube so that continuous images appear on a monitor while the C arm is rotated, whereby an operator can observe the stereoscopic dynamic images or acquire DSA images taken from a plurality of directions.
As one of general methods for obtaining a completer X-ray three-dimensional image, there is known a method in which tomographic images obtained by an X-ray CT apparatus are connected to each other through image processing. This method however has had a problem that the X-ray CT requires a lot of imaging time.
For the purpose of reducing the imaging time, there is advantageously used a cone-beam CT apparatus in which a 2-dimensional X-ray detector is used as an X-ray detector and 2-dimensional transmission images of a subject obtained through X-ray beams emitted from an X-ray source in a cone shape are use to reconstruct a 3-dimensional X-ray image of the subject.
Disclosed in a journal entitled "Medical Imaging Technology", Vol. 10, pp. 113-118, 1992 is a cone-beam CT apparatus wherein a 2-dimensional X-ray detector is made up of an X-ray image intensifier and a television camera.
Also disclosed in a paper entitled "Development of 3D CT with a large area detection system" of a journal "Radiology", Vol. 185(P), p. 271, 1992 is a large-view-field cone-beam CT apparatus wherein a 2-dimensional X-ray detector is made up of a large-area phosphor screen and a television camera.
Known a typical algorithm of reconstructing a 3-dimensional image of a subject in a cone-beam CT apparatus is the Feldkamp's method (refer to a paper "practical cone-beam algorithm" of a journal "Optical Society of America," written by L. A. Feldkamp, et al., A/Vol. 1(6), pp. 612-619, 1984).
There are also described in IEEE Transactions on Medical Imaging, Vol. 12, No. 3, pp.486-496, 1993 a method in which an imaging unit including an X-ray source and an X-ray detector is rotated around a subject and at the same time the subject is moved in a direction perpendicular to a rotation plane to enlarge a view field with respect to the rotation-axis direction of the subject, as well as a reconstruction algorithm thereof.